Bone marrow mesenchymal stromal cells attenuate smoke inhalation injury by regulating the M1/M2-Th17/Treg immune homeostasis axis

Smoke inhalation injury (SII) is the leading cause of death in fire burn patients. The inflammatory response induced by smoke inhalation is a significant factor in the development of acute lung injury or acute respiratory distress syndrome (ALI/ARDS). Mesenchymal stem cells (MSCs) can alleviate various inflammatory diseases by regulating the polarization of macrophages from the M1 to the M2 phenotype. Moreover, MSCs can facilitate the inflammatory response by regulating Th17/Treg homeostasis. However, little is known about the associations among MSCs, M1/M2 macrophages and Th17/Treg homeostasis. Therefore, the purpose of this study was to evaluate whether MSCs affect subsequent Th17/Treg differentiation and immune homeostasis by regulating M1/M2 polarization in SII. Our results showed that bone marrow mesenchymal stem cells (BMSCs) ameliorated lung inflammatory injury and fibrosis after SII by affecting the polarization of alveolar macrophages (AMs) from the M1 to the M2 phenotype. Moreover, BMSCs maintain Th17/Treg immune homeostasis by increasing the proportion of Treg cells and decreasing the proportion of Th17 cells. In vitro, we further demonstrated that BMSCs promoted the polarization of AMs from the M1 to the M2 phenotype and decreased IL-23 levels. Reduced IL-23 decreased Th17 differentiation and promoted Th17/Treg balance. Therefore, BMSCs ameliorate the inflammatory response and lung damage after SII through regulating M1/M2 polarization and subsequent Th17/Treg immune homeostasis, which are linked to alveolar macrophage-derived IL-23. These findings provide novel insight into how BMSCs regulate the M1/M2-Th17/Treg immune homeostasis axis and provide new therapeutic targets for more effective control of the inflammatory response after SII.